The present invention relates to semiconductor transducers and more particularly an accelerometer formed using semiconductor microcircuit technology.
In recent years there have been vast changes in aircraft avionics systems which require more sophisticated and highly accurate sensors for aircraft control. While electronic circuits have improved significantly, the mechanical structures required to convert such things as pressure, temperature and acceleration have become obsolete. As a result, increasingly sophisticated electronic systems are being used with relatively old mechanical devices for measuring physical parameters. Such a mismatch of technologies fails to take advantage of the many improvements in the electronic circuitry, thereby limiting the accuracy, sensitivity, and reliability of the systems.
In the area of accelerometers particularly, aircraft manufacturers and vendors of aircraft equipment have long relied on electromechanical sensing of acceleration. The conventional electromechanical devices generally include a moving vane and torque coil which is coupled to a sensing circuit and amplifier for registering acceleration changes upon movement of the torque coil. Such devices have long been used to provide a gross measurement of acceleration. However, the same devices suffer from various deficiencies which limit their use with sophisticated electronic systems.
One of the problems which has plagued the electromechanical structure is its susceptibility to aircraft vibration which decreases or destroys the accuracy of electromechanical sensing circuits. The vibration is particularly acute when the natural frequency of aircraft engines approaches the same frequency as the accelerometer. In modern aircraft, the natural frequency of the engines appears to be substantially the same as that of the electromechanical accelerometers. The resulting resonance therefore limits the accuracy and lifetime of the instrument.
Electromechanical accelerometers also suffer from calibration and temperature inaccuracies. It has been found that there is generally no standard for calibration of accelerometers. There is therefore an inability to provide an accurate correlation between the instruments, even when purchased from the same source. As a result, accelerometers are not interchangeable and cannot be accurately recalibrated. Vendors have further neglected to significantly improve the response of their sensors to varied temperature and external conditions. As a result, there is now a need to provide hermetically sealed instruments to reduce sensitivity and reliability problems, but the techniques for sealing have not been explored sufficiently to allow production of acceptable devices.
The use of the electromechanical accelerometers originated when aircraft operation was limited to relatively low altitudes. Accordingly, the temperature and other environmental conditions to which the accelerometers are now exposed at high altitudes prevents their reliable operation. In addition, the cumbersome and complex electromechanical structures are costly which limits their appeal for use in new avionics systems. There is therefore a need to provide highly reliable, low-cost transducers which can measure acceleration and be compatible with present electronic control systems.
Accordingly, the present invention has been developed to overcome the shortcomings of the above known and similar techniques and to provide a solid-state accelerometer capable of low-cost fabrication with microcircuit technology.